Needleless syringe comprising an optimized injector-receptacle

ABSTRACT

The invention relates to the realm of needleless syringes used for injecting liquid active substances. Said syringe comprises a reservoir that is enclosed by means of displaceable plugs which trap the liquid. The reservoir is initially isolated from an injector-receptacle ( 37 ) which is provided with at least two peripheral injection conduits ( 38 ) that are arranged outside the receptacle ( 37 ). Said receptacle ( 37 ) encompasses a pocket bore ( 31 ) which accommodates the plug located downstream such that the optimized inlets ( 39 ) of the conduits are unobstructed. The face of the receptacle ( 37 ), which is located upstream, comprises a multilobed sealing joint ( 34 ) which is disposed parallel to and as close as possible to the edges of the bore ( 31 ) and the inlets ( 39 ). The aim of the invention is to create an injector-receptacle ( 37 ) that is optimized regarding discharging and the resistance thereof to the injection pressure.

The present invention falls within the field of disposable needlelesssyringes; such syringes are used for intradermal, subcutaneous andintramuscular injections of liquid active principle for therapeutic usein human or veterinary medicine.

A first requirement of such needless syringes is that of long-termcompatibility between the liquid active principle and the reservoirwhich contains it. Another requirement is to have a reservoir that istransparent so that the correct filling of the reservoir can be checkedbefore the syringe is used. These requirements lead to the production ofessentially transparent reservoirs made of a material compatible withthe active principle for the desired length of time: this is generallyborosilicate glass for pharmaceutical use: glass of type I or II.

The initial phase of the injection is critical to the penetration intothe skin of the jet or jets of liquid, depending on whether the syringehas one or several injection ducts. The latter configuration beingfavorable to reducing the discomfort. The final bioavailability dependson this initial phase being performed correctly; it assumes that theliquid in the injection ducts is quickly brought up to speed withoutmultiple jerkiness in the jets when the water hammer effect is too greatfor this rapid acceleration.

Patent application WO 01/58512 describes a needleless syringe comprisinga reservoir closed by movable upstream and downstream plugs entrapping aliquid active principle; said reservoir is initially isolated from aninjector or receptacle which comprises at least two injection ductssituated on its outer lateral face and a blind central bore in which thedownstream plug becomes housed in such a way as to uncover the inlets tothe injection ducts as the downstream stopper/active principle/upstreamstopper assembly is moved through the action of a driving device inorder to perform the injection.

A first difficulty with this syringe is that the inlets to the injectionducts are not optimized. They are not optimized, on the one hand, withrespect to pressure drops and, on the other hand, with respect toresidual liquid losses in the dead volumes. In that application, theinlets are radial grooves over the entire upstream face of thereceptacle. Finally, the shape of the upstream opening of the centralbore is not optimized and may tear the downstream stopper when thelatter engages therein.

An important problem is not satisfactorily solved in that invention, andthat is the problem of minimizing the pressure forces on the receptacleduring the injection phase in the knowledge that these forces are ofdecisive importance to the receptacle. Given the configuration produced,the entire surface of the receptacle bearing against the reservoir issubjected to the pressure because the sealing is transferred off towardthe binding material on the outside of the reservoir because the use ofan O-ring seal is impossible here particularly because of the radialinlet grooves to the injection ducts.

The present invention sets out to solve the problems of optimizing theinlets to the injection ducts and above all those of reducing thepressure forces on the receptacle during the injection phase.

The present invention relates to a needleless syringe comprising a bodyhousing a cylindrical reservoir closed by a movable upstream stopper anda movable downstream stopper entrapping an active principle andcomprising, downstream, an injector-receptacle termed more brieflyreceptacle with at least two peripheral injection ducts, said receptaclebearing against the reservoir and comprising a blind bore the freeheight of which allows the inlets to the peripheral ducts to beuncovered when the downstream stopper is brought into contact with theclosed end of the bore of said receptacle through the operation of adriving means moving the upstream stopper/liquid/downstream stopperassembly, and said syringe is characterized in that each inlet comprisesa spot face positioned on the injection duct and is connected to aradial channel opening into the central bore. As a preference, said spotface is centered on the injection duct.

In this application, the qualifier “downstream” is used to denote anycomponent close to the injection site or any part of a component facingtoward this injection site; this site is the patient's skin. Bycontrast, the qualifier “upstream” will be used for any componentdistant from the injection site or any part of a component facing awayfrom this site. Thus, the receptacle comprises a downstream face facingtoward the patient's skin and an upstream face which is opposite it andbears against the reservoir; these downstream and upstream faces areconnected by a lateral face.

For this invention, a liquid active principle or drug is essentiallyintended to mean a liquid of some viscosity, or a mixture of liquids, ora gel. The active principle may be a solid dissolved in a solvent suitedto injection. The active principle may be a solid in pulverulent formplaced in suspension, of greater or lesser concentration, in anappropriate liquid. The particle size of the solid active principle andthe shape of the duct need to be tailored to avoid blockages.

The reservoir, which is essentially cylindrical, is made of type I ortype II glass; however, it may be made of any other material that istransparent and compatible with the active principle. The upstream anddownstream faces are essentially flat, the planes containing them beingperpendicular to the axis of symmetry of the reservoir. The upstream anddownstream faces bear respectively on the body of the syringe and thereceptacle. The bearing faces of these two components have seals thecharacteristics of which will be specified later on.

An injection duct crosses the entire height of the receptacle from theupstream face to the downstream face. The injection ducts, because thereare at least two of these, are said to be peripheral because they arearranged in the receptacle around the blind central bore. Theycommunicate with said central bore only via inlets describedhereinafter. The injection duct has a cross section that may vary fromupstream to downstream on the one hand for reasons associated with itsproduction and on the other hand in order to obtain a jet that is fineand rapid enough to penetrate the patient's skin to the desired depth.In general, the injection ducts are identical, uniformly distributedabout the blind central bore and have axes parallel to the axis of thereceptacle, but they may also be different.

The driving means which will act on the upstream stopper may be amechanical motor: expansion of a compressed spring, or a spring of thepneumatic type: expansion of a compressed gas, or a pyrotechnic gas:expansion of a combustion gas.

The way in which the syringe works is as follows: the driving means willact on the upstream stopper and move the upstreamstopper/liquid/downstream stopper assembly because the liquid isincompressible. The downstream stopper moves and becomes housed in theblind bore of the receptacle until it comes into contact with the closedend of said bore. The height of this bore is such that, when thedownstream stopper is in contact with the closed end of said bore, theinlets to the injection ducts, on the periphery of the bore of thereceptacle, are uncovered; the liquid is discharged into them and isinjected by the movement of the upstream stopper which continues untilthe reservoir is emptied: the upstream stopper is then in contact withthe downstream stopper.

The inlet to an injection duct, which inlet is situated on the upstreamface of the receptacle, comprises a spot face positioned and preferablycentered on the injection duct and a radial channel connecting said spotface to the blind central bore of said receptacle.

The spot face forming the inlet to the injection duct has a diameterranging between about 1.1 times and about 1.5 times the diameter of theinjection duct, and preferably about 1.2 times this diameter. Thediameter of the duct taken here for reference is the diameter near theupstream face of the receptacle. The depth of the spot face rangesbetween about 0.5 times and about 0.7 times the diameter of theinjection duct and is preferably about 0.6 times this diameter.

A radial channel, connecting to the aforementioned spot face, connectsthe bore to the injection duct. The depth of said radial channel isequal to that of the spot face. The width of this radial channel iseither constant and equal to the diameter of the spot face or this widthincreases from the width it has where it meets the spot face to a highervalue where it opens into the central bore: this higher value will,however, remain smaller than about 1.4 times the diameter of theinjection duct.

The spot face may be understood in its customary technical sense: thatis to say as a machined feature in the form of an upright circularrecess made around a hole, in which case the lateral face of the spotface is perpendicular to the flat upstream face of the receptacle and tothe closed end of the spot face.

However, a spot face may also be understood in a broader sense in whichthe lateral face of the recess is no longer perpendicular but obliquewith respect to the upstream face and even meets the closed end of therecess in the form of a rounded corner. In this case, the dimensions ofthe spot face and of the radial channel will be measured at theirupstream part.

The upstream face of the receptacle comprises a central orificeconsisting of the blind central bore and the inlets connecting said boreto the injection ducts. The edges of this orifice are the intersectionsof the flat upstream face and of the lateral faces of the bore and ofthe inlets. Theoretically, these edges correspond to fairly sharp edges,but these edges are blunted with an appropriate radius of curvatureespecially on the portions which are the edges of the central bore andthose of the intersection of the radial channels so as not to damage ortear the downstream stopper when it engages in the central bore at thestart of operation and passes “over” these portions.

This upstream face comprises a multilobed seal parallel and as close aspossible to the edges of this central orifice. The seal is said to beparallel to the edges because its distance to the edge, evaluated in adirection perpendicular to the edge, is constant, the seal is said to beas close as possible to the edge because this distance is as short aspossible given the ways in which the receptacle is formed. The seal ismultilobed because it surrounds on the outside the inlets to theinjection ducts while being parallel and as close as possible to theedge; in this instance, the idea of on the outside being evaluated interms of remoteness from the axis.

By comparison with a circular seal surrounding the bore and the inletsto the ducts, the multilobed seal as defined reduces the surface area ofthe receptacle that is exposed to the pressure of the liquid during theinjection phase because, in the case of the sectors between the ducts,the multilobed seal is closer to the edge of the bore than a circularseal.

According to a first embodiment, the multilobed seal is an added seal,housed in a groove of mating shape made on the upstream face of thereceptacle. This embodiment entails fitting the seal in the groove usingprecise methods then precise handling operations to mount it bearingagainst the reservoir, then in the body of the syringe.

According to a preferred second embodiment, when the receptacle isproduced by injection molding, the multilobed seal as previouslydescribed is produced by two-shot injection molding. The multilobed andtwo-shot injection molded seal has a central additional thickness on itsexterior face; the compression and deformation of this additionalthickness as the receptacle and the reservoir are pushed togetherensures sealing.

The two-shot injection molding technique, known from elsewhere,consists, when the main component, in this case the receptacle, has beeninjected and has not yet hardened, in taking it up again and, using anappropriate mold, injecting the material that will produce themultilobed seal into the cavity provided for this purpose in thereceptacle. This cavity must of course be parallel to the edges of theorifice and as close as possible to the edge. This technique can belikened to the technique of overmolding the multilobed seal.

The two-shot injection molded multilobed seal has the advantages ofyielding, almost directly after this second injection, a singlereceptacle/seal component so that the assembly of the syringe thencontinues.

Advantageously, the central bore of the receptacle is of essentiallyfrustoconical shape, the inlet diameter of said bore being equal to theinside diameter of the reservoir and the smallest diameter of the borebeing toward the closed end of said bore, a running generatrix of thelateral part making an angle of between about 2° and about 9° with theaxis of symmetry of the bore and this angle is preferably about 7°. Theclosed end of the bore connects to the lateral part with an appropriaterounding.

The depth of the bore is such that, when the downstream stopper isbearing against the closed end of the bore, the inlets to the injectionducts are uncovered and place the reservoir in communication with theinjection ducts. The relatively open shape of the bore means that thedownstream stopper enters this cavity and deforms uniformly during thisphase, thus deadening the shock and limiting the forces on thereceptacle during this phase of the operation.

The present invention applied to a prefilled one-use syringe has theadvantage of allowing a separation to be made, within the device,between two parts. One part which will be termed the pharmaceutical partcomprising the body and the reservoir with the movable upstream anddownstream stoppers and possibly the injector/receptacle: thissubassembly may be processed under the conditions of the pharmaceuticalindustry, particularly in terms of sterilization and asepsis.

This subassembly will be integrated into the remainder of the syringe,the elements of which have been assembled elsewhere, this assembly beingperformed under conditions which are not as strict as those associatedwith the pharmaceutical industry.

When the downstream stopper is housed in the bore of the receptacle, thesyringe becomes very difficult to reuse. This arrangement therefore alsohas the advantage of preventing said syringe from being reused forpurposes other than the initial therapeutic use.

Finally, this configuration has the advantage of avoiding any possibleleaks of liquid through the injection ducts before the injection isadministered. What happens is that the device is frequently agitated,this even sometimes being recommended in order to examine the clarity ofthe liquid or in order to homogenize the mixture when the liquidcontains particles in suspension. The fact that the active principle isisolated, prior to injection, from the ducts affords ultimate protectionagainst this risk of loss.

The invention is set out in detail hereinbelow with the aid of figuresdepicting various particular embodiments of the invention.

FIG. 1 depicts a longitudinal section through a syringe according to afirst embodiment of the invention.

FIG. 2 is an enlargement of the downstream part of said syringe.

FIG. 3 is a perspective view of another exemplary embodiment of thereceptacle according to the invention.

FIG. 4 depicts a section through said receptacle on a plane passingthrough the central axis of the receptacle and containing the axis of aninjection duct.

FIGS. 5, 6 and 7 schematically and in perspective depict various shapesof inlets to the injection ducts.

FIG. 1 depicts, in partial longitudinal section, a syringe according tothe invention; it is depicted vertically, the injection system pointingdownward which will be the downstream direction.

The syringe 1 comprises a body 2 in which there is housed a reservoir 3containing the liquid active principle 6. Placed at the downstream endof the body 2 is a receptacle 7 comprising, for example, three injectionducts such as the duct 8. The injection system is covered with externalprotection to ensure the asepsis of the syringe: this protectioncomprises an elastomer membrane pressed against the exterior face of theinjector by a fine metal disk crimped around this end of the syringe.This protection will be removed before injection. At its opposite end,the body 2 of the syringe is fixed to a driving means 70 which, in thisexample, is a pyrotechnic gas generator; this will be described lateron. The reservoir 3 presses against the body 71 of the driver 70,sealing being afforded by a circular O-ring seal.

The body 2 of the syringe comprises two diametrically opposed aperturesfor viewing the active principle contained in the reservoir 3: these aresimply two oblong openings in the body. At the downstream end of thebody 2 of the syringe there is push fitted, into a bore of appropriateshape, a cylindro-conical receptacle 7 which will be describedhereinafter. Pressing against this receptacle 7 and centered in thedownstream end of the body 2 there is a glass reservoir 3; thisreservoir is a tube. Upstream, the body 2 of the syringe accepts thebody 71 of the driving means which is centered around the other end ofthe reservoir. The reservoir 3 is essentially a tube closed at both endsby movable upstream 4 and downstream 5 stoppers; these stoppers arepreferably piston plungers customarily used in syringes: these arecomponents obtained by the molding of elastomers that have long-termcompatibility with the active principle: each component incorporates thepiston and sealing functions through the producing of bulges or lips(not detailed in the figures). The elastomers customarily used formanufacturing these components are, for example, chlorobutyls orbromobutyls, the Shore hardness of which is set between about 45 andabout 70. These components may receive surface treatments particularlyto make them easier to move in the tubular reservoir. In the free state,the piston plunger has a diameter about 10 percent greater than theinside diameter of the tube that will accommodate it, and the height ofthe piston plunger is about 0.5 to 0.8 times this diameter. When thepiston plunger is engaged in the tube, because of the deformations, itsheight is equal to about 0.6 times to about 1.0 times the insidediameter of the reservoir.

In this example, the receptacle 7 is a component of cylindro-conicalexterior shape which comprises a central bore 10 in which the downstreamstopper 5 will be accommodated. On its periphery, the receptacle hasthree injection ducts just one of which, identified as 8, is visible inthis section. The diameter of the bore is equal to that of thereservoir. The free height of the blind bore 10 of the receptacle 7 isequal to that of the downstream stopper 5 mounted in the reservoir 3.When the downstream stopper 5 has reached the closed end 7 a of thereceptacle, the inlet 9 (on the reservoir 3 side) of the injection ducts8 is placed in communication with the liquid 6; the liquid flows at aspeed corresponding to the pressure transmitted by the upstream stopper4.

In this embodiment, the driving means acts on the upstream stopper byway of a piston 11 the effective cross section of which is equal to thatof the upstream stopper 4. This piston 11 is in contact with theupstream stopper 4 and there is therefore no shock or hammer effect atthe beginning of operation. This piston 11 by virtue of its sealingsystem prevents the gases produced by the combustion of the charge 72from coming into contact with the upstream stopper and thereforeprevents any possible damage to the latter or leakage of gas toward theactive principle contained in the reservoir. This piston 11, of asuitable color, may also serve as an indicator of operation by beingvisible in the viewing apertures in the body 2 of the syringe.

We shall now describe the main elements of the pyrotechnic generator 70.It comprises, in the body 71 above the piston, a pyrotechnic charge 72the combustion of which is initiated by a primer 73 impacted by astriker 74. The primer 73 is housed in a primer holder. In the initialposition, the striker 74 is held, in the striker guide 75, securelyscrew-fastened to the body 71, by at least one ball, such as the ball77, partially engaged in a groove in the striker. The percussion devicecomprises a push button 78 with a groove 79 and an internal spring 76.

The push button 78 slides over the outside of the striker guide 75 andis held in place by pins 80 running in lateral slots 81. This pushbutton 78 here is the triggering member.

Of course, in order to initiate combustion of the pyrotechnic charge 72,without departing from the scope of the invention, it is possible to useinitiation devices other than the device involving a striker describedhere. Without wishing to be exhaustive, we mention by way of exampleinitiation devices involving an electric battery, or piezoelectricallyinitiated devices.

The pyrotechnic gas generator could be replaced by a gas generatorconsisting of a reservoir of compressed gas closed by a rapidly openingvalve. The triggering member will open said valve, the compressed gasesin the reservoir will expand and act on the pushing means.

For use, having removed the asepsis cap, and placed the downstream faceof the injector onto the skin of the subject to be treated, the operatorusing his or her thumb presses the push button 78 which depresses,compressing the spring 78. The push button moves until the groove 79comes level with the groove of the striker 74, the balls, such as theball 77, that hold the striker 74, move aside into the groove 79 andrelease the striker which will violently strike the primer 73,initiation of which ignites the pyrotechnic charge 72. The striker 74bearing against the primer holder 30 holds the primer in place andensures sealing: the combustion gases do not travel back toward the pushbutton.

The combustion of the pyrotechnic charge will produce gases which act onthe piston 11.

FIG. 1 depicts a syringe according to the invention, in the form of apen: all the elements have the same central axis but are superposed.Without departing from the scope of the present invention, otherarrangements are conceivable, for example the driving part may be at acertain angle to the reservoir/receptacle part in order to achieve morecompact shapes like the one described for example in patent applicationFR 2 815 544.

FIG. 2 is an enlargement of the downstream part of the syringe alreadydescribed.

The receptacle 7 is a component of cylindro conical exterior shape pushfitted into the body 2 of the syringe.

The blind central bore 10 is essentially cylindrical. As a preference,the upstream edge, meeting the upstream face of the receptacle and thebore, comprises a rounded portion with enough of a radius of curvaturethat the downstream stopper is not torn when it enters the bore at thestart of operation.

The receptacle comprises several injection ducts of which just one,identified as 8, is visible in this view. An inlet 9 connects the bore,more precisely the upstream part of said bore, to the injection duct.When the downstream stopper is entirely housed in the bore, liquid,which comes to occupy the upstream part, can flow as far as theinjection duct.

It is possible to see a sectioned view of a multilobed seal 12 placed ina seal groove which is as close as possible to the edges of the bore andsurrounds the spot face. This aspect will be described in greater detailhereinafter.

FIGS. 3 and 4 depict another embodiment of a receptacle of a syringeaccording to the invention. In this example, the receptacle is obtainedby injection molding a polycarbonate compatible with the envisioned use.

Said receptacle 37 comprises, on its lateral face, a lateral screwthread for screw fastening into a body of appropriate shape. Thereceptacle comprises three peripheral injection ducts, of which justone, 38, is visible in the sectioned view. The three injection ductsare, in this example, identical and uniformly distributed about thecentral bore 31 of the receptacle; they are connected to said bore byinlets 39. Given the method of manufacture, by injection molding, of thereceptacle, the upstream part of the duct is fairly wide, about 0.8 mmin diameter over about 4 mm to about 5 mm in height, this portion iscylindrical or cylindroconical; it is extended in the downstreamdirection by a narrower part with a diameter of about 0.1 mm and about 2mm to about 3 mm high, to produce the jet which will penetrate thepatient's skin to a greater or lesser depth.

In this embodiment, the upstream face of the receptacle comprises aclipping device 40 which will accept and hold a reservoir comprisingbulges at its ends; said reservoir may be prefilled before it is mountedon the receptacle; this stand alone assembly in this example constitutesthe pharmaceutical part of the syringe; it may be handled as anindependent entity. This device is described in greater detailelsewhere.

The upstream face of the receptacle comprises a three-lobed seal 34because there are three injection ducts in this example. This seal ismanufactured by two-shot injection molding. The three-lobed seal isparallel and as close as possible to the edges of the bore and to theedges of the inlets in the sense that we have defined earlier.

The sectioned view shows that the cavity accepting the three-lobed sealis of rectangular section. The three-lobed seal occupies this entirecavity with an additional thickness 35 in the central part of its freeupstream face because the reservoir has not yet been mounted on thereceptacle.

In order to anchor the three-lobed seal more firmly in the cavity of thereceptacle, the downstream face of the seal has uniformly distributedanchoring pegs which become housed in orifices prepared in the cavity atthe time of the injection-molding of the receptacle. Such a peg 36 canbe seen on the opposite side to the injection duct.

The elastomer chosen for the two-shot injection molding of the seal mustadhere appropriately to its support; this is one of the benefits of thetwo-shot injection molding technique; it must also be capable of longendurance and its hardness must be sufficient to fulfill the sealingfunction. A Shore hardness of about 75 is suitable for this application.When the receptacle is made of polycarbonate, the elastomer of the sealmay be Santoprene®.

In this example, the blind central bore is of frustoconical shape withan angle of about 7°.

The inlet diameter, that is to say the upstream of the receptacle of thebore, is equal to the diameter of the reservoir.

The edges of the bore: intersection of the upstream face of thereceptacle and frustoconical part of the bore do not intersect to form asharp edge but these faces are connected with a suitable curvature thatcan be seen in FIG. 4.

Likewise, the edges of the radial channel: intersection of the radialchannel and of the bore is rounded, with a smaller radius of curvaturethan in the previous case.

FIGS. 5, 6 and 7, which are partial perspective schematic views, showvarious embodiments of the arrangement of the inlet to an injection ductof a receptacle according to the invention. In these figures, the partswhich are analogous are denoted by the same references as were used inFIGS. 3 and 4.

FIG. 5 shows a first embodiment of an inlet 39 with a spot face 59centered on the injection duct 38 and a radial channel of constant widthconnecting the spot face and the central bore. In this example, thesides of the spot face and of the channel are perpendicular to theupstream face of the receptacle and to the closed end 19 of the inlet39.

FIG. 6 shows another embodiment which differs from the previous onethrough the channel which is wider at the bore and converges somewhat tomeet the spot face 59 centered on the injection duct 38.

FIG. 7 shows an embodiment with a channel of constant width, but thesides of the channel and of the spot face 59 are not perpendicular butare rounded to meet the closed end region 19 of the channel and of thespot face with a large radius of curvature; this is an inlet device ofprofiled section.

In these three diagrams, for the sake of simplicity, the intersections,on the one hand, between the bore and the upstream face of thereceptacle and, on the other hand, the bore and the radial channels aredepicted by arcs of a curve which give the impression of sharp edges; inpoint of fact, these sharp edges are blunted by sufficient curvature forthe connections.

1. A needleless syringe, comprising: a body having a downstream end; acylindrical reservoir having opposite ends and housed by the body; amovable upstream stopper; and a movable downstream stopper closing theopposite ends of the cylindrical reservoir and entrapping an activeprinciple, the movable downstream stopper comprising: a receptacledisposed at the downstream end of the body, the receptacle having anupstream face and at least two peripheral injection ducts each havinginlets, said receptacle bearing via its upstream face against thereservoir, the receptacle further having a blind central bore; a drivingmeans for moving the upstream stopper, the downstream stopper, and theactive principle, wherein a free height of the blind central bore allowsthe inlets to the peripheral ducts to be uncovered when the downstreamstopper is brought into contact with a closed end of the bore of saidreceptacle through the operation of the driving means, and wherein, onthe upstream face of the receptacle, each inlet comprises a spot facepositioned on the respective injection duct and is connected to a radialchannel opening into the blind central bore, and the upstream face ofthe receptacle comprising a multilobed seal substantially parallel tothe edge of the bore and substantially surrounding the inlets to theinjection ducts.
 2. The needleless syringe as claimed in claim 1,wherein said multilobed seal is housed in a groove of mating shape. 3.The needleless syringe as claimed in claim 1, wherein the upstream faceof the receptacle comprises a two-shot injection molded multilobed sealsubstantially parallel to the edge of the blind central bore andsurrounding the inlets to the injection ducts as closely as possible. 4.The needleless syringe as claimed in claim 1, wherein the spot facecentered on the injection duct has a diameter ranging between about 1.1times and 1.5 times the diameter of the injection duct and a depthranging between about 0.5 times and about 0.6 times the diameter of theinjection duct.
 5. The needleless syringe as claimed in claim 4, whereinthe radial channel has a constant width equal to the diameter of thespot face.
 6. The needleless syringe as claimed in claim 4, wherein theradial channel has a width that increases from its point of connectionto the spot face to its opening into the blind central bore where itswidth is at most equal to 1.4 times the diameter of the spot face. 7.The needleless syringe as claimed in claim 4, wherein the spot face andthe radial channel are “profiled”.
 8. The needleless syringe as claimedin claim 1, wherein the blind central bore is of essentiallyfrustoconical shape, the inlet diameter of the bore being equal to theinside diameter of the reservoir, the smallest diameter being toward theclosed end of the bore and a running generatrix of the frustoconicallateral part making an angle of between about 2° and about 9° with theaxis of the bore.
 9. The needleless syringe as claimed in claim 8,wherein the upstream edges of the blind central bore and of the inletshave curvatures so as not to tear the downstream stopper.
 10. Theneedleless syringe as claimed in claim 2, wherein the spot face centeredon the injection duct has a diameter ranging between about 1.1 times and1.5 times the diameter of the injection duct and a depth ranging betweenabout 0.5 times and about 0.6 times the diameter of the injection duct.11. The needleless syringe as claimed in claim 3, wherein the spot facecentered on the injection duct has a diameter ranging between about 1.1times and 1.5 times the diameter of the injection duct and a depthranging between about 0.5 times and about 0.6 times the diameter of theinjection duct.
 12. The needleless syringe as claimed in claim 5,wherein the spot face and the radial channel are “profiled”.
 13. Theneedleless syringe as claimed in claim 6, wherein the spot face and theradial channel are “profiled”.
 14. The needleless syringe as claimed inclaim 2, wherein the blind central bore is of essentially frustoconicalshape, the inlet diameter of the bore being equal to the inside diameterof the reservoir, the smallest diameter being toward the closed end ofthe bore and a running generatrix of the frustoconical lateral partmaking an angle of between about 2° and about 9° with the axis of thebore.
 15. The needleless syringe as claimed in claim 3, wherein theblind central bore is of essentially frustoconical shape, the inletdiameter of the bore being equal to the inside diameter of thereservoir, the smallest diameter being toward the closed end of the boreand a running generatrix of the frustoconical lateral part making anangle of between about 2° and about 9° with the axis of the bore. 16.The needleless syringe as claimed in claim 4, wherein the blind centralbore is of essentially frustoconical shape, the inlet diameter of thebore being equal to the inside diameter of the reservoir, the smallestdiameter being toward the closed end of the bore and a runninggeneratrix of the frustoconical lateral part making an angle of betweenabout 2° and about 9° with the axis of the bore.
 17. The needlelesssyringe as claimed in claim 5, wherein the blind central bore is ofessentially fi-ustoconical shape, the inlet diameter of the bore beingequal to the inside diameter of the reservoir, the smallest diameterbeing toward the closed end of the bore and a running generatrix of thefrustoconical lateral part making an angle of between about 2° and about9° with the axis of the bore.
 18. The needleless syringe as claimed inclaim 6, wherein the blind central bore is of essentially frustoconicalshape, the inlet diameter of the bore being equal to the inside diameterof the reservoir, the smallest diameter being toward the closed end ofthe bore and a running generatrix of the frustoconical lateral partmaking an angle of between about 2° and about 9° with the axis of thebore.
 19. The needleless syringe as claimed in claim 7, wherein theblind central bore is of essentially frustoconical shape, the inletdiameter of the bore being equal to the inside diameter of thereservoir, the smallest diameter being toward the closed end of the boreand a running generatrix of the frustoconical lateral part making anangle of between about 2° and about 9° with the axis of the bore.